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				son = document.getElementById('son');

				son.nextSibling.style.fontSize="50px";

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		<div id="father" class="box">
			<p id="son">学并思</p><p>学并思</p>

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		<div class="box1">
			<p>学并思</p>
			<p>学并思</p>

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		<div class="box">
			<p id="box">学并思</p>
			<p>学并思</p>

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